Turbine propeller control system



March 20, 1956 R. c, TRESEDER ET AL 2,738,843

TURBINE PROPELLER CONTROL SYSTEM Filed Feb. 25, 1955 INVENTOR. Noe 70N Bevo/11s Arroz/ve Ys United States Patent 2,738,843V ',TURBINE PROPELLER` CONTROL SYSTEM Robert C.`Tre`seder and Morton 'Broolrs, Dayton, Ohio, and RichardE. Moore, Los Angeles, Calif., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware p y Application February 25, 1953, Serial No. 338,758 i (Cl. Utl-135.74)

The present invention `relates to a control system for an engine-propeller,` combination, Yand rmore particularly to a method and means for controlling a turbine driven variable pitch propeller. y In aircraft propelled byv turbine propeller combinations it is often necessary for the pilot to make split second decisions and, instantaneous manipulations of the controls to avoid mishap. An error due to misjudgment v `or inadvertence in some instances may result in damage to the craft. In an effort to `obviate some of these difficulties and at least mitigate the necessity'of critical con,- trol manipulations, this invention allows the pilotadditional time to correctfor engine malfunctions, such as failure, that occur during critical operating conditions,for example, when taking off from a landing surface. Accordingly, our objects include the provisions of a method and means for controlling the 'possible rate of blade angle change in accordance with the throttle position, and the further provision of such means enabling higher rates of blade angle change at partially open throttle and lower rates of lblade angle change at fully open throttle.

The aforementioned and other objects are accomplished in the present invention by providing means where-` by the pressure differential between a source of"pressureV uid and servo actuated means for changing blade angle,4

which differential determines thepossible rate of blade angle change, is dependent upon the throttle position Tas determined by a master control lever. Specifically, the invention comprehends the provisionl ofpressure control means in a iluid pressure system for controlling and effecting variation of the blade pitch position in a -variable pitch propeller. The fluid pressure system for altering the blade pitch position includes a source of tluid under pressure, pressure controlling means, blade actuating servo means and valve means for controlling the Vflow of uid, such as oil, to and from the servo means. The rate of blade angle change, in the disclosed embodiment, is dependent upon the potential of pressure applied to the servo means. In this type of system the rate of blade angle` change may be altered by varying the pressure differential existent between the source of pressure iluid and the blade servomeans. The rate of blade angle change will be maximum when the aforesaid dierential is high and minimum when the differential is low. This phenomenon occurs by reason of `the pressure differential being dependent upon the cumulative pressure ydrops resultant from flow through the system in accordance with well known principles of hydraulics.

In the present invention the pressure controlling means constitutes a valve having means for varying the spring load thereon in accordance with the position of a coordinated master control lever, the position of which is determinative of engine power and the engine throttle position. In this regard the spring load is increased at partially` open throttle and decreased at fully openthrottle, as will appear more fully hereinafter. l

Further objects and advantages of the present inven-l tion will be apparent from the following description in i o be obtained by other means, reference to which will be ICC which the drawing represents a schematicdiagram of a fluid pressure system constructed in accordance with this invention.

With particular reference to the` drawing, it will be apparent that the present invention is exemplified in conjunction with a fluid pressure system for controlling and effecting changes in the blade angle position of a variable pitch propeller having a pump 10 as the source of pressure fluid, a pressure controlling valve assembly 20, a distributor valve 3Q and a shuttle valve 40, which are interconnected by passages to form a circuit for directing fluid flow to and from a blade angle actuator or servo means 50. Structurally, the fluid pressure system and blade angle actuator may take the form shown in the Blanchard et al. Patents 2,307,101 and 2,307,102. It is to be understood that themethod envisaged by the present inventionis independent of the particular lluid pressure system herein disclosed in that variation inthe rate of blade4 angle change, measured rin degrees of blade movement about their longitudinal axes per second, can

alluded to hereinafter.

As aforementioned, the problem sought to be solved by 4this invention is to provide a control system for a turbine driven variable pitch propeller which will provide `the pilot with additional time to correct for engine failures 'that'occur during critical operating conditions. The critical operating condition may, for example, occur when the aircraft is vtaking off, at which time, the throttle is ordinarily fully open. If the engine should fail with the throttlepfully open during a take ol and the propeller is under the control of a governor, such as that disclosed in Serial No. 94,984, filed May 24, 1949, in the name of Dinsmore et al., the governor would automatically tend to decrease the propeller pitch at theV maximum rate of blade angle change permitted by the fluid pressure system. In installations of this character no means are provided for varying the maximum rate of blade angle change inac'cordance with throttle position. Accordingly, the pilot must immediately sense the engine failure and render theV governor inoperative in order to avoid mishap. However, by following the teachings of this invention, additional time for the pilot to vconsider what step is to be taken will be provided by correlating the possible rate of blade angle change with the engine throttle position. f

In accordance with the well known principles of hydraulic flow through a system including tubes and oriices, the pressure losses caused by ow. through a system are proportional to the velocity of llow in the system. As the rate of blade angle change in degrees per second is dependent upon the quantity of ilow to the blade angle changing servo means, it is apparent that the pressure drop through the system is likewise proportional to the rate of blade angle change. Accordingly, in a pressure system havingv a source of fluid under pressurev interconnected through valves 'with a servo unit or actuator, the rate of movement of the actuator will be maximum when the pressure differential between the source of supply and the servo means is high, and the rate will be minimum when the differential is low.

In the disclosed embodiment the pressure differential between the source of supply and the blade actuating servo meansfis controlled in accordance with the throttle position of the engine by varying the spring load in a pressure control valve assembly. In accordance with the disclosed embodiment the spring load is less at full throttle than it is at partially open throttle. However, it is appar-y ent that other means would perform equally as well in carrying out the disclosed method, such as controlling the orilce or port openings of a distributor valve in accordance with throttle position, or utilizing a variable displacementpump `as thesouree'of fluid under pressure. Itis. readilywapparent.thatl if.smaller. orificewopeningsfare permitted at partially opentthan are permitted at fully open throttle, the pressure differential between the source of supplyandfthe servo means willl likewise vary inversely with thethrottle position. Moreover, iflthe pump displacement is greater than at partially open throttle'than atffully open throttle,`thefpressuredifferential between the source'of supplyand the servo means will likewise vary inversely with-regard to the throttle position.

Referring again to the drawing,the pump it? operates continuously to'supply'uid under'pressure to trunk line ltduring propeller rotation. lThe pump "has an inlet passagelZ, whichconnects withral suitable reservoir, not shoWn,an"d an outlet-passage lf3 connected through a check valve 14 to `the trunk line 1l. Trunk'line '11 communicates with'the pressure control valve assembly Zl'through'line'l, and also communicates with a supply port 16 of .the distributor valve 30. Control ports 17 and 13 of the distributor valve 30 are connected, respectively, by lines 19 and 21to opposed chambers of blade actuating servo means V50.

The pressure existent in trunk line 11 is controlled by the pressure control valve assembly 2t), which embodies an equal area valve 22 having a variably loaded spring 23. The equal area valve is housed in a casing 24 and comprises a plunger normally urged by the spring 23 toward the upper end of housing 24, as shown in the drawing. Line 15 communicates with a chamber 26 in casing 24 within which aland 27 of the plunger 25 is disposed. Chamber 26 has a relief port 28 therein which relief port may be closed by upward movement of the plunger 25 Aunder the urge of spring 23. The amount which relief port 28 is open determines the .pressure existent in trunk line 11. That is, if .the relief port 28 is fully closed by land'27, the pressure existent in trunk line 11 will be equal to the pressure output of pump 10. However, the pressure potential existent in trunk line 11 will be reduced proportionally to the opening of port 28I permitted by land 27. Pressure fluid in chamber26 of. casing 24 tends to move the plunger 25 downwardly, as viewed in the drawing, so that land 27 will open relief port 28, by acting on the upper surface of land 27. However, downward movement of the plunger 25 is opposed by the combined forces of spring 23 and pressure tiuid existent in chamber 29, which acts on the lower surface of land 27, the upper and lower surfaces of land 27 being of equal'area.

The pressure potential existent in chamber 29 of the equal-,areaivalverassemblytis thehigher of the pressures existent in eitberlines 19 .or .21, which connect the distributor valve 30 to the-servo means 50. .Lines.19 and 21 are connected,respectively, by lines 31 and 32 to opposite sides of the shuttlevvalve 40, which comprises a valve casing 53 having azchamber 34, which in a shuttle valvefmemberispositioned under the urge of the pressure fluid existentin either of lines 31 or 32. The higher ofthe-pressures existent in lines 19 and 21 will be transmitted through either of lines 31 or 32 to the chamber 34 from whence it will be transmitted through line 36 to the chamber y29 ,of the `pressure control valve assembly 20. .Thepressure in chamber 29 of the pressure control valve assembly `20 assists the spring 23 in urging the plunger 25 upwardly in a manner tending to close port 28. However, upward-movement of the plunger 25 is opposed `by `the pressure potential existent in trunkline 11 asv communicated to chamber`26 by line 15. Thus, the demandfforgpressure 'fluid `by v.the servo :means 50 is transmitted to-t'ne vequal area -valve `22'to1actuate the equal area -valveso that-the pressure 'requirements ofthe unit 50 incarrying out its control function will be met by tliepurnp 10.

l`Flow'fromthe trunk line 11`to opposed chambers `of theservo means 50 is controlled bythe distributor vvalve el O 30 which includes a valve guide 36 having the supply pond-@andthecontrolportsellandlS. VMDisposed-within the valve guide 36 is a valve plunger 37 having spaced lands 38 and 39, which cooperate respectively with control ports 17 and 18 to control the flow of fluid there through. The plunger 37 is connected by a mechanical linkage 41 to a blade anglecontrol lever 52. A master control lever 42 isconnected by=alinkage^43 tocan engine throttle positioner 44, as well as by linkage 45 to a cam surface 46.

Cum surface 46 is Aengaged by a cam followert47 attached to a rod 48 which extends through'the casing 24, and has a platform 49 disposed within the chamber 29. One endof'the1spring23'seats 'against the tupper surface of platform 49, while the other .end of spring 23 seats against'thelo'wer surface of'a platform 51 formed on the plunger' 25. It is readily apparent that lineal movements of the cam surface 46 will result in varying the load on spring 23 of the pressure control valve assembly 20. In the instant disclosure'the loadl on spring 23 is increased by moving cam surface 4'6 to the'left when the master control lever 42 is moved to reduce the opening of the engine throttle through the throttle positioner '44 of an engine driving the propeller, not shown. Conversely, when the lever 43 is moved toincrease the'throttle opening of the engine, the load on spring 23 is decreased by moving the cam surface '46 to the right, yas viewed in `the drawing. As hereinbefore mentioned, normally propeller pitch is automatically controlled by governor means which may be of the type shown in the aforementioned copending application. These governing means control uid owfrom trunk line 11 to lines 19 and -21 leading to the ser-vo means 50 independent of the distributor valve 30. However for simplification, only the distributor valve 30 is shown in the drawing in order topoint out the-invention with greater particularity.

ln operation, with the control lever 42 set at fully open throttle position, the load on spring 23 will beata minimum. Accordingly, the pressure transmitted to chamber 29 of the pressure control valve assembly 20 will beunable to effect movement of plunger 25 suiicient to fully close relief port 28. Thus, the pressure differential between trunk line 11 and either lines 19 or 21 will be at avminimum and, accordingly, the possible rate of blade angle change will be minimum. ln this instance should an engine failure occur, additional time will be afforded the pilot whereby he may manipulate control lever 52 to actuate the distributor vvalve plunger 37 to leflect movement of the propeller blades to the desired position. As the throttle controlled by lever-42 is moved toward the closed;position,'the load on spring 23 will be gradually increased whereupon the pressure existent in chamber l29 will be assisted to a greater degree by the spring 2-3 rin tending to move the plunger .25 fto a position whereland 27 will-close relief port 28. As critical operating'conditions :with a turbine propeller combination lgenerally occuratfully open throttle, there is no necessity for;pro viding additional time for the pilot to deliberate should the engine fail at partially open throttle. Accordingly, the lpressure differential between trunk line 11 andteither of trunk lines 19 or 21 may beincreased to a maximum value by the closure of relief port 28 by land 27 when the throttle is partially open. ln this manner the maximum possible rate of blade angle change is available when the engine throttle is only partially opened.

From the foregoing it is apparent that this'invention discloses a method and one form of apparatus for con trolling the possible rate of blade angle change according to the throttle position'of an engine. This system, which allows higher rate of blade angle change at partially'open throttle and lower rates of blade angle change at fulbI openthrottlel is thought to present a practical solution to one of the problems existent in turbine propeller combinations.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In an engine propeller combination having a fluid pressure system including a source of Huid under pressure and servo actuated means for varying the blade angle position of a variable pitch propeller, and a throttle for controlling the engine, the combination including a circuit interconnecting said source and said servo actuated means, first valve means in said circuit between said source and servo actuated means for controlling the flow of pressure uid to and from said servo actuated means, second valve means between said source and rst valve means for controlling the pressure potential of fluid applied to said servo actuated means by said first valve means, and throttle position controlled means for continuously adjusting said second valve means throughout substantially the full range of throttle movement so that higher pressure potentials are permitted at partially open throttle than are permitted at fully open throttle.

2. In an engine propeller combination having a lluid pressure system including a source of fluid under pressure and servo actuated means for varying the blade angle position of a variable pitch propeller, and a throttle for controlling the engine, the combination including a circuit interconnecting said source and said servo actuated means includinga pressure line and blade angle control lines, valve means in circuit connection between the pressure line and the blade angle control lines, and lthrottle position controlled means for continuously varying the pressure diterential between said supply line and said blade angle control lines throughout substantially the full range of throttle movement Vto control the rate of blade angle change in accordance with throttle position.

3. In an engine propeller combination having a fluid pressure system including a source of uid under pressure and servo actuated means for varying the blade angle position of a variable pitch propeller, and a throttle for controlling the engine, the combination including a circuit interconnecting said source and said servo 'actuated means including, a pressure supply line and blade angle control lines, first valve means in circuit connection between the pressure supply line and the blade angle control lines, second valve means connected with said supply line be-` tween said source and said rst valve means, said second valve means controlling the pressure potential existent in said supply line, and throttle position controlled means operatively connected with said second valve means for continuously varying the maximum obtainable pressure potential in said supply line throughout substantially the full range of throttle movement, whereby the pressure differential between said supply line and said blade angle control lines will vary inversely with engine throttle position.

4. In an engine propeller combination having a fluid pressure system including a source of uid under pressure and servo actuated means for varying the blade angle lposition of a variable pitch propeller, and a throttle for controlling the engine, the combination including, a circuit interconnecting said source and said servo actuated means including a pressure supply line and blade angle control lines, rst valve means in circuit connection between the pressure supply line and the blade angle control lines, second valve means connected to said pressure supply line between said source and said first valve means, said second valve means controlling the maximum obtainable pressure potential existent in said supply line and including a spring loaded member, and throttle position controlled means for continuously varying the spring load on said member throughout substantially the full range of throttle movement so that higher rates of blade angle change are permitted at partially open throttle than are permitted a fully open throttle.

5. In an engine propeller combination having a fluid pressure system including a source of fluid pressure and a fluid motor for varying the pitch position of a variable pitch propeller, and a throttle for controlling the engine, the combination including, pressure regulating means operatively connected with said source of iluid pressure and said motor and operable to control the pressure diierential existent between the source of iluid pressure and the fluid motor for controlling the rate of pitch change, and means operatively interconnecting said throttle and said pressure regulating means for continuously adjusting said pressure differential throughout substan- -tially the full range of throttle movement.

6. In an engine propeller combination having a uid pressure system including a source of uid under pressure and servo actuated means for varying the blade angle position of a variable pitch propeller, and a throttle for controlling the engine, the combination including, a circuit interconnecting said source and said servo actuated means, a control valve in said circuit between said source and said servo actuated means for controlling the ow of pressure fluid to and from said servo actuated means, pressure regulating means operatively connected with said source of fluid pressure and said servo actuated means and operable to control the pressure differential existent between said source and said servo actuated means for controlling the rate of pitch change, said pressure regulating means comprising a valve having opposed equal areas subjected to the pressure of said source and the pressure of said servo actuated means, and means operatively interconnecting said throttle and said pressure regulating means for continuously adjusting said pressure diierential throughout substantially ythe full range of throttle movement.

7. The combination set forth in claim 6 wherein said pressure regulating means includes a spring acting upon said valve for biasing said valve in one direction.

8. The combination set forth in claim 7 wherein the means operatively interconnecting said throttle and said pressure regulating means comprises a throttle positioned cam and a cam follower engaging said spring for varying the stress thereof.

References Cited in the tile of this patent UNITED STATES PATENTS 2,550,529 Carson et al. Apr. 24, 1951 2,600,017 Morris 'et al. lune 10, 1952 2,649,161 Carson et al. Aug. 18, 1953 FOREIGN PATENTS 955,854 France Jan. 20, 1950 

